A beam-down solar concentrator with a fixed focus — Design and performance analysis

Abstract

In this study, a two-stage beam-down dish solar concentrator with a fixed focus was innovatively designed, consisting of a paraboloidal primary reflector (PR), a flat secondary reflector (SR), and a receiver. A new sun-tracking mode was proposed to obtain a fixed focus. The influences of the PR rim angle, SR tilt angle, and distance from the SR to the primary focus on the concentration ratio and optical efficiency using different types of SR (flat or hyperboloidal reflectors) were comprehensively investigated. The instantaneous and overall optical performances were determined using Monte Carlo ray-tracing simulations. The results showed that the optimum SR tilt angle is equal to 38.25° as the solar altitude angle ranges from 30° to 73.5°, and the optimum PR rim angles are 45° and 60° for the two proposed concentrators adopting a flat SR (Design I) and a hyperboloidal SR (Design II). The numerical values of instantaneous and overall optical performance for Design I and Design II are almost equal, whereas the flat SR adopted in Design I is preferred in terms of manufacturing accuracy and installation. A peak solar concentration ratio of 6970 suns and an overall average of 2097 suns are achieved over the 35 mm-radius aperture of the receiver for Design I. The radiative power and overall optical efficiency are 8.089 KW and 78.9%, respectively.